(1) Field
The field of the present invention relates to devices and methods for detecting ground loops, more particularly to the field of devices and methods for detecting ground loops using hand-held, portable exciters and receivers, and still more particularly to devices and methods for detecting ground loops using hand-held, portable AC exciters and receivers that are sensitive to the inductance of ground loops.
(2) Related Art
Ground loops occur when electrical or electronic equipment are interconnected so as to develop unwanted paths to ground. There are many reasons for the existence of ground loops; they might be due to an accidental connection to ground (ground fault) or may be due to an inadvertent shortcoming of the system design. Regardless of the cause of ground loops, currents can flow in these loops, resulting in spurious, unwanted, and often confusing signals; these signals due to ground loops interfere with low-level signals typical of laboratory environments and instruments. In extreme situations, currents flowing in ground loops can even be dangerous, damaging equipment and endangering personnel.
Ground loops are not only a problem in research laboratories but also in the video and audio recording industries, temperature and humidity sensors used in building automation, medical diagnostics, and in the home where interconnected audio/video systems are notorious for producing ground loops.
Ground loops are especially hazardous in pulsed-power systems, such as plasma and fusion experiments, because the large and rapidly changing stray magnetic fields in these systems can induce enormous transient voltages. In addition, ground loops in pulsed-power systems are notoriously hard to find because of the transient nature of the pulsed magnetic fields.
Locating ground loops is conventionally accomplished by disconnecting suspect cables until the ground loop disappears. This diagnostic method can be tedious if there are large numbers of cables and becomes impractical if more than one ground loop exists because, in such a case, disconnecting any single cable will not reveal the ground loop. In the situation of multiple ground loops, all cables would have to be removed and then reconnected one-by-one until a ground loop appears. Obviously, disconnecting large numbers of cables tends to disable equipment, making it difficult to simultaneously generate a ground loop and search for it. In complex situations, the ground loop might never be found.
Compounding matters, the complexity and topology of ground loops may vary with the frequency of the signals flowing in them. At low frequencies, small resistances of cables tend to be responsible for ground loops, whereas, at high frequencies, it is the impedance of cables that tend to be responsible for ground loops. Thus, any system that searches for the existence of ground loops must do so at a frequency similar to that of the signals flowing in the system.
Information relevant to attempts to address these problems can be found in references Ref. 1 through Ref. 7, cited below. However, each one of these references suffers from one or more of the following disadvantages: requiring physical, invasive contact to circuits, such as soldering or clipping; operating at a frequency which is too low to measure the inductive impedance and thus the size of ground loops; lack of portability or incapable of being “hand-held”; requiring computers or complicated algorithms to operate; consuming too much power to be battery-operated; using large amounts of high-permeability magnetic materials, requiring increase costs; being quite large, further increasing costs; lacking a “binary” response to ground loops; and overcoupling the detector to ground loops, which tends to change the circuit under test. For the foregoing reasons, there is a need for a ground loop locator that: has a non-perturbative probe; operates at high frequencies where the impedance of a ground loop is highly inductive, giving an indication of the physical size of ground loops; is hand-held and portable; can be easily operated and read; consumes a low enough amount of power that it can be battery-operated; is inexpensive; is small; has a “binary” response to ground loops; and probes ground loops without changing their properties.